Sub‐Single‐Crystal and Grain‐Boundary Bonding Strategy for Superior Battery Stability

Abstract Ultrahigh‐nickel cathodes have become a promising option for high‐performance lithium‐ion batteries (LIBs). However, traditional ultrahigh‐nickel secondary particles often crack at the interfaces between primary grains, causing significant surface side reactions. On the other hand, single‐crystalline particles face issues like long lithium‐ion diffusion paths and surface reconstructions. To address these challenges, this study introduces a sub‐single‐crystal structural strategy designed to shorten lithium‐ion diffusion paths within the particles and uses a grain‐boundary bonding technique to reduce the risk of secondary microsphere fracturing due to uneven mechanical stress. Specifically, 1 µm LiNi 0.93 Mn 0.07 O 2 single‐crystal particles are bonded with Li 3 BO 3 to create secondary particles. These smaller single‐crystal particles not only reduce the diffusion distance but also improve Li+ transport channels at grain boundaries. The bonding layer effectively limits electrolyte–electrode contact, prevents harmful grain phase changes, and boosts the cycle stability of the electrode material. In full battery tests with graphite anodes at a 1 C‐rate, the capacity retention rate is nearly 90% after 800 cycles at room temperature and about 82% after 800 cycles at 60°C. These results show that the structural design strategy greatly enhances structural stability. This research provides a solution for ultra‐high nickel cathodes, offering strong potential for advancing their practical applications.